1. Field of the Invention
The present invention relates to a magnetic phase shifter control system, and more particularly to a magnetic phase shifter control system suited to construct an automatic control system.
2. Description of the Prior Art
Magnetic phase shifters have been widely used in an automatic control system for main motors of vehicles, e.g. thyristor controlled electrical vehicle, because they have many advantageous features. For example, they are simple and strong in construction, they can add and subtract a number of control inputs while they are isolated from each other, they can amplify and convert a signal resulting from the addition and the subtraction into a phase shifting signal, and they are not easily influenced by noise.
By way of example, U.S. Pat. No. 3,914,672 entitled "Chopper Control System" discloses a system in which a magnetic phase shifter is used to control a chopper which in turn drives a D.C. motor of the electric vehicle or the like. The magnetic phase shifter used therein includes a saturable core, a control winding to which a current command for the D.C. motor is applied, a feedback winding to which a current of the D.C. motor is fed back, a bias winding to which a predetermined biasing signal is applied, a shorting winding for stabilizing the characteristic, an output winding for producing a signal having a phase in accordance with the current command, and an A.C. power supply for exciting the output winding. The magnetic phase shifter controls a duty factor of the chopper in accordance with the current command. It presents no particular inconvenience so long as it is operated in a normal amplification region.
However, where the magnetic phase shifter is to be operated while shifting the operation region thereof from a remanent output region to the normal amplification region, it presents inconvenience. Namely, when the operating region is shifted from the remanent output region to the normal amplification region, a dead time occurs at the boundary. Here, the "dead time" means a phenomenon in which an output cannot follow an input and there occurs a time delay before a normal output is produced.
It is known that the higher the amplification degree in the normal amplification region is and the larger the shorting effect of the shorting winding is, the longer is the dead time. For example, the Japanese Patent Publication No. 37-6075 published in June 26, 1962 and entitled "Method for Selecting Cores for Magnetic Amplifier" includes description on page 1, left column, lines 6 to 11, which suggests that the larger the amplification degree is, the larger is the dead time, and the article of the paper No. 831 of the 1963 Joint conference of Four Electrical Associations of Japan, entitled "Time Delay Utilizing a Jump of A Magnetic Amplifier" includes description in a preamble thereof which suggests that the larger the shorting effect of the shorting winding is, the larger is the dead time.